This invention relates to projection systems which xe2x80x9ctilexe2x80x9d multiple projector images on a rear projection screen, and more particularly to a cost effective method for high performance rear projection screen manufacturing and a seamless rear projection screen produced thereby.
Flat panel displays are commonly employed in lap-top, notebook or other portable computers in which packaging dimensions are of critical importance. In such applications, it is particularly important to keep the thickness of the display system to a minimum.
In prior display systems, minimum display thickness is obtained by employing a flat, minimum illumination source. The illumination source often comprises a flat fluorescent light system and a contiguous diffuser that are positioned adjacent to the rear surface of an active matrix liquid crystal module. The diffuser is utilized in an attempt to distribute light from the fluorescent source evenly over the liquid crystal module. In viewing the displayed image, the viewer effectively looks through the liquid crystal module at the diffused light source behind it.
With this method, it is very difficult to provide uniformity of brightness over a large surface area of the display. Further, because the viewer is effectively looking through the liquid crystal display at the diffuse light source behind it, light rays that pass through the liquid crystal display at an angle will traverse a longer path through the liquid crystal material than those that pass through at a normal to the display surface. This results in image contrast degradation.
A display system utilizing a collimated light source to illuminate a liquid crystal light valve (LCLV) and a rear projection diffusing screen in front of the LCLV to diffuse the light and control the field-of-view of the display system, particularly the use of collimated light to illuminate the LCLV, avoids the contrast problems discussed above. However, the display thickness must be at least as great as the projection screen width due to the need to collimate the illumination light before it reaches the LCLV. This limits the applicability of the display system to flat panel displays with relatively small screen sizes.
One way of overcoming this screen size limitation is to display the image as a set of individual smaller image portions that are displayed side-by-side in an array fashion on the rear projection screen. Each of the smaller image portions is created with separate small image sources, such as LCLV. This technique, known as xe2x80x9ctilingxe2x80x9d, allows one to create a display system with an arbitrarily large screen size, while still employing a number of relatively small image sources. An example of tiling of images is shown at FIG. 1.
Seamless tiling of the rear-projected multiple images seems to be the most effective way to create a large area, high-resolution display. However, the properties of the diffused screen cause a directional non-uniform scatter (as shown at FIG. 2), so special solutions are required in order to reach seamlessness.
One problem with tiled systems is non-uniformity in brightness between the adjacent image portions on the projection screen when viewed either on or off-axis. This is because the brightness of an image that is diffused from a rear projection screen varies as a function of both the angle incidence that the image makes with respect to the projection screen, and the angle at which the observer views the image on the projection screen. Since each of the tiled images is incident on the screen at a different angle, and since an observer views each of them at a different viewing angle, the observer will perceive brightness differences between them.
The known solutions include a diffused screen with a large (up to 50%) degree of image overlap or combination of various pre-screens with diffused screen resulting in lesser or no image overlap. Referring to FIG. 3, one of the most effective pre-screens known is a fused fiber optic face plate FIG. 3, which works as a multiple channel spatial integration tube. Referring to FIG. 4, in combination with a diffused screen, a fiber optic faceplate simulates a Lambertian screen. Application of fused fiber optic face plate has been described in U.S. Pat. No. 5,626,410, incorporated herein by reference. Fused fiber optic faceplates are also commercially available from Schott Fiber Optics, Inc., InCom USA, Inc. and Collimated Holes, Inc. Manufacturing of a fused fiber optic faceplate is a highly labor consuming and expensive process. This state of the art has not had a commercial application because of a very high cost and limited sizes of the fused fiber optic faceplate available. The largest possible size is one square foot.
Fused fiber optic faceplates cannot be seamlessly tiled to produce a larger faceplate. xe2x80x9cDeadxe2x80x9d fibers on the boundaries of a fiber optic faceplate cause visible black seams on the boundary, which are apparent when a fiber optic faceplate is tiled with one or more additional faceplates. These visible black seams are shown in the photograph at FIG. 5.
Fused fiber optic faceplates cannot be combined to form a larger faceplate for use as a pre-screen because they cannot be seamlessly tiled. Therefore, there is a need for a faceplate which has no size limitations, and can be seamlessly tiled.
In one embodiment, the present invention provides a seamlessly tiled projection display comprises at least one lab-created crystal faceplate as a pre-screen in combination with a diffused rear projection screen. In one embodiment multiple plates of crystals may be seamlessly tiled into a larger plate, satisfying the need for a large projection screen.
In one embodiment the optical faceplate is made from fibrous crystals which are transparent, colorless and work as a coherent faceplate. In one embodiment, the numeric aperture of a single fiber is within a range of about 0.20 to 0.66, depending upon the application of the optical faceplate. In one embodiment the crystals form as a conglomerate of aligned fibers which align in parallel, and possess a high transparency in the long dimension of the fibers. The crystals are environmentally stable and non-toxic. A nonlimiting example of such a fibrous crystal is Ulexite (also known as xe2x80x9cTVxe2x80x9d rock), found in abundance in nature. Examples of other minerals having similar qualities are Selenite, Artinite and Aragonite.
These minerals, in their naturally occurring form often have defects and impurities. Therefore, in one embodiment the present invention comprises an optical faceplate made of these minerals in lab-created, artificially grown form. In a further embodiment, an optical faceplate is made of crystals not found in nature, or not found in nature in fibrous form.